Extra garden granted by council

We recently bought a house in La Marina and the council have fenced off an extra area which we can use as a garden. I understand we cannot build any permanent structures or do any building work. We were thinking of laying slabs for a patio and maybe constructing a small wall for plants but a friend said this might be illegal as it could be classed as building work. If so, we will put stones down assuming this is allowed. Does anyone know the rules on this or maybe there is a leaflet explaining things. Thank you, for your help.